Lafayette HE-74 User manual

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VARIABLE
FREGUENCY
OSCILLATOR
OPERATING
MANUAL

TECHNICAL SPECIFICATIONS
FREQUENCY COVERAGE.,
FUNDAMENTAL
OSCILLATOR
FREQUENCY
....
OUTPUT FREQUENCY
Ce
OUTPUT POWER ......
eS
OUTPUT IMPEDANCE.,.......
a
TUBE COMPLEMENT
Ce ey
Ce
Ce
3.5- 4,00 Me.
7.0- 7,30 Mc,
14.0-14,35 Mc.
21.0-21.45 Mc.
28,0-29.70 Mc,
50.0-54,00 Mc,
3.5 -4,0 Mc for 80M and 10M bands,
3.5 -3.65 Me for 40M, 20M and 15M bands
4,.16-4.50 Mc for 6M band.
80M band: 3.5 -4.00 Mc.
40M band: 7,0 -7,.30 Me.
20M band: 7.0 -7.175 Me,
15M. band: 7,0 -7,15 Me,
10M band: 7,0 -7,425 Mc,
6M band: 8,333-9,00 Mc,
10-30 volis RMS
LOW 52 ohms, HIGH 50K ohms,
Vl 6BA6 Series-tuned Clapp Oscillator,
V2°6BA6 Broad-Band Buffer-Amplifier.
V3 6AQ5 Output Amplifier,
V4 VRI50MT/OA2 Voltage Regulator
117 volts 50-60 cps AC,
Height 7-3/4"; Width 8-3/4"; Depth 10",
13-1/4 lbs,
COPYRIGHT 1963 BY LAFAYETTE RADIO ELECTRONICS CORP.
Printed in U.S.A,
IM-360 6/63 IM/K

GENERAL DESCRIPTION
The HE-74 is a rugged Variable Frequency Oscillator designed for dependable, stable operation on all
bands from 80 through 6 meters, with sufficient output to drive any multi-estage"transmitter of modern
design,
For high stability, the VFO employs a series-tuned Clapp oscillator, incorporating special tempera-
ture-compensating capacitors. The oscillator uses three fundamental tuning ranges to provide suit-
able outputs for the six amateur bands, The fundamental tuning ranges are as follows:
(1) 3.50-4.00 Mc.
(2) 3.50-3,65 Mc,
(3) 4.16-4,50 Mc,
The chart below shows how these basic tuning ranges are used;:-
FUNDAMENTAL
OSCILLATOR VFO
TUNING OUTPUT
3,50 - 4.00
(2) 3,50 - 3.65 Mc
(2) 3,50 - 3.65 Mc
(2) 3,50 - 3.65 Mc
(1) 3.50 -4,00 Mc
(3) 4,16-4,50 Me
3,50 -4,00 Mc (Fundamental used)
7,00 -7,30 Me (2nd Harmonic used)
7.00 -7,175 Mc (2nd Harmonic used)
7,00 -7.15 Me (2nd Harmonic used)
7.00 -7.425 Mc (2nd Harmonic used)
8.333 -9,00 Mec (2nd Harmonic used)
The second stage performs as a broad-band buffer-amplifier on 80 through 6 meters, It offers good
isolation between the output and the oscillator and thus prevents any frequency shift due to load varia-
tions, A special switch position also permits this stage to function as a crystal oscillator to provide an
output for calibrating purposes,
The output stage operates as an amplifier to provide a high output signal level for connection to the
transmitter, The plate circuit is arranged to provide optimum tuning to the fundamental oscillator
frequency on 80 meters and to the second harmonic on 40 through 6 meters (see table above). The out-
put terminates in two coaxial connectors -- one providing a low impedance output, the other a high im-
pedance output,
The power supply uses a low-heat silicon rectifier in a half-wave circuit with good filtering. A voltage
regulator tube maintains stability by eliminating any effect on the oscillator due to line voltage variations
Rigid mechanical construction has been employed throughout. Double-bearing construction is used on
the tuning capacitor, All frequency determining components are enclosed in a separate compartment to
maintain rigidity, shielding, and provide isolation from heat-producing elements in the circuit,
Although the HE-74 is compatible with most amateur transmitters having a VFO input, it was designed
primarily to match the LAFAYETTE KT-390 Transmitter, both electrically and in styling. Any questions
regarding the compatibility of this VFO with units which do not have a VFO input should be directed to
the transmitter manufacturer, who is best qualified to give such information.
INSTALLATION
POWER
The VFO operates from 105-120 volts, 50-60 cycles AC. Do not use on any other power source,
OUTPUT CONNECTIONS
The
VFO
is
equipped
with
two
outputs,
One
is
a
high
impedance
output,
while
the
other
is
a
low
imped-
ance
output,
In
cases
where
it
is
necessary
to
use
a
connecting
cable
longer
than
36
inches
between
the
VFO
and
transmitter,
use
the
low
impedance
output.
For
cable
lengths
of
36
inches
or
less,
use
the
high
impedance
output,
Note,
however,
that
when
using
the
low
impedance
output,
it
will
be
necessary
to
add
a
decoupling
capacitor
of
about
2000
upyf
in
series
with
the
VFO
input
on
the
transmitter.

irordé¥
to
connect
the
VFO
to
your
transmitter,
you
will
need
coaxial
cable
and
terminating
plugs,
as
indicated
below;
RG-62/U
coaxial
cable,
PL-259
type
connector,
UG-175/U
type
adaptor,
RCA-type
phono
plug
(for
VFO
input
on
transmitter),
Instructions
for
attaching
a
coaxial
connector
to
one
end
of
coaxial
cable,
anda
phono-type
plug
to
the
other
end
(if
your
transmitter
VFO
input
has
a
phono
jack),
have
been
included
for
your
convenience,
LOCATION
Install
the
VFO
as
close
to
the
transmitter
as
possible,
Avoid
very
warm
locations
and
allow
at
least
one
inch
between
the
rear
of
the
VFO
anda
wall,
DIAL
CALIBRATIONS
The
VFO
dial
uses
six
calibrated
scales
for
tuning
on
80,
40,
20,
15,
10
and
6
meters,
The
calibration
indicate
the
RF
carrier
frequency
of
the
transmitter
Output
stage,
not
the
VFO
output,
The
table
below
shows
how
each
scale
is
calibrated:
VFO
Scale
80M
40M
20M
15M
10M
6M
Minor Calibrations
Every
Major Calibrations
Every
OPERATING INSTRUCTIONS
1,
Set
the
VFO
Function
switch
to
STANDBY
and
set
the
Band
switch
to
the
desired
band
of
operation,
2,
Place
the
transmitter
in
the
Standby
position
and
allow
both
units
to
warm
up
for
30
minutes,
3,
Tune
the
VFO
to
the
desired
frequency
as
indicated
on
the
calibrated
dial,
Refer
to
the
chart
below
which
shows
the
actual
VFO
output
frequencies
for
various
dial
settings,
Also
indicated
is
the
transmitter
multiplication
necessary
in
each
case
to
produce
an
RF
carrier
output
which
matches
the
VFO
dial
tuning,
If
operation
on
14,00
Mc
were
desired,
for
example,
the
VFO
band
switch
should
be
set
to
20M
and
the
VFO
tuned
to
14,00
on
the
20M
scale,
The
output
frequency
of
the
VFO
would
actually
be
7,00
Mc,
However,
setting
the
band
switch
on
the
transmitter
to
20M
oper-
ation
will
normally
provide
a
doubling
action
and
thus
produce
a
14,00
Mc
RF
carrier
output,
CHART
MULTIPLICATION
AMATEUR
VFO
DIAL
ACTUAL
VFO
REQUIRED
BY
BAND
SCALE
OUTPUT
FREQ.
TRANSMITTER
80M
3.50-
4,00
Mc*
3,50
-4,00
Me
None
40M
7,00-
7.30
Mc
7.00
-7,30
Me
None
20M
14,00
-
14,35
Mc
7.00
-7,175
Mc
X2
15M
21,00
-
21,45
Mc*
7.00
-7.15
Mc
x3
10M
28,00
-
29,70
Mc%
7.00
-7.425
Mc
xX4
6M
50.00
-
54,00
Mc
8.333-9,00
Me
X6
*
The
VFO
calibrations
actually
extend
beyond
these
band
Limits.
However,
the
range
shown
covers
only
the
amateur
band
in
each
case.

4, Set the VFO to SEND.
5,
Switch
the
transmitter
to
its
operating
position
and
follow
the
manufacturers
recommended
tuning
procedure,
;
VFO CALIBRATION
The
VFO
has
been
carefully
aligned
at
the
factory
and
should
therefore
offer
accurate
calibration
at
all
dial
settings,
Remember,
however,
that
it
is
always
the
operator's
responsibility
to
guard
against
operation
outside
of
the
amateur
band
limits.
A
procedure
for
checking
and
adjusting
the
calibration
is
provided
in
the
section
headed
"VFO
CALIBRATION".
VFO CALIBRATION
The
HE-74
was
accurately
calibrated
at
the
factory
before
shipment.
However,
with
prolonged
use
or
after
servicing,
it
may
become
necessary
to
readjust
to
VFO
for
accurate
calibration,
OUTPUT ADJUSTMENT
1,
Connect
a
#47
pilot
lamp
across
the
LOW
output
jack
as
indicated
below,
attach under
¥47PL
screw
head
solda
Insert in center
contact of jack
2,
Turn
the
VFO
function
switch
to
SEND,
band
switch
to
80M
and
set
tuning
pointer
to
3.50
Mc,
3,
Adjust
TC4
for
maximtim
brilliance
of
the
pilot
lamp.
See
bottom
of
VFO
fer
adjustment
points,
4, Disconnect the pilot lamp.
CALIBRATING ADJUSTMENTS
The
calibrating
procedure
is
a
relatively
simple
one
which
can
be
carried
out
using
a
3.5
Mc
and
an
8.333
Mc
crystal,
As
an
example,
the
procedure
for
checking
calibration
on
the
80M
band
is
given
below,
)
1,
Closely
couple
the
VFO
output
to
the
receiver
antenna.
Do
not
make
a
direct
connection,
however.
All
adjustment
points
are
indicated
on
the
underside
of
the
VFO,
Make
adjustments
through
the
holes
provided,
using
a
non-metallic
alignment
tool,
2,
Insert.
a
3.50
Mc
crystal
into
the
socket
in
the
VFO,
3,
Set
the
VFO
Function
switch
to
STAND
BY
and
allow
the
VFO
and
your
receiver
to
warm
up
for
about
30
minutes.
4,
Set
the
VFO
Function
switch
to
CAL,
band
switch
to
80M,
Detune
the
VFO
--
away
from
the
crys-
tal
frequency
or
any
of
its
harmonics,
5, Tune the receiver to the crystal oscillator signal on 3,5 Mc,
6,
Set
the
VFO
tuning
pointer
(exactly)
to
3.50.
If
VFO
tuning
is
precisely
on
frequency,
the
signals
of
the
main
VFO
oscillator
and
the
crystal
oscillator
will
produce
a
''zero
beat"
in
the
receiver.
Check
this
by
slightly
detuning
the
VFO,
If
a
"zero
beat"
is
not
obtained
when
the
VFO
pointer
is
set
exactly
to
3,50,
the
calibration
is
slightly
off
and
you
should
adjust
TCl
as
indicated
in
the
VFO
Calibration
Chart.

7,
Follow
this
same
general
procedure
on
80,
40
and
6M
bands
bration
and
make
adjustments
where
necessary,
VFO CALIBRATION CHART
Function
Switch to
CAL
CAL
CAL
Band
Switch
VFO Pointer
Set to
Receiver
Tuned to
3,50 Me
7,00 Me
8.333 Mc
Remarks
Adjust for "zero
beat'' in receiver
*
This
adjustment
also
brings
the
10M
band
into
line.
**
This
adjustment
also
brings
the
20
and
15M
bands
into
line.
ATTACHING
COAXIAL
CONNECTOR
&
ADAPTOR
TO
COAX
CABLE
(RG-58/U,
29/U,
62/0)
en
3
* 32
COUPLING RING ADAPTER
1,
Cut end
of
cable
even,
Remove
vinyl
jacket
21/32''--
don't
nick
braid,
Slide
coupling
ring
and
adaptor
on
cable,
2, Fan braid slightly and fold back over
cable,
3. Compress braid around cable, Posi-
tion adaptor to dimension shown, Press
braid down over body of adaptor to dimen-~
sion shown, Press braid down over body
.of adaptor and trim,
4, Bare 1/2" of center conductor -~- don't
nick
conductor,
Pre-tin
exposed
center
conductor,
SOLDER HOLE
5,
Screw
the
plug
assembly
on
cable,
Solder
plug
assembly
to
braid
through
solder
holes,
Solder
conductor
to
con-
tact
sleeve,
Remove 1" of outer insulation, It may be
necessary to slit the insulation lengthwise
to remove, Take care not to cut shield
wires,
Push the shield back as far as it will go
and strip off 3/4" of insulation from the
inner conductor.
Place phono connector on cable firmly
against inner insulation, Solder inner
conductor,
Dress shield up on base of connector and
solder, Then trim inner conductor from
tip,
(as
shown
in
the
chart)
to
check
cali-

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